A highly sensitive indirect spectrophotometric red-ox method for the determination of osmium is reported.The method is based on the oxidation of iodide by osmium(Ⅵ)and the spectrophotometric detection of the liberated iodine in the form of complex anion and ion associate with 2-(4-diethylaminostyryl)-1,3,3-trimethyl-6-nitro-3H-indolium chloride reagent.The appropriate reaction conditions have been established.The molar absorptivity is(1.6-5.6)×10~4 L mol~(-1)cm~(-1).Beer’s law holds for the concentration range of 0.5-11.4μg mL~(-1)of Os(Ⅵ). A highly sensitive indirect spectrophotometric red-ox method for the determination of osmium is reported. The method is based on the oxidation of iodide by osmium (VI) and the spectrophotometric detection of the liberated iodine in the form of complex anion and ion associate with 2 - (4-diethylaminostyryl) -1,3,3-trimethyl-6-nitro-3H-indolium chloride reagent.The appropriate reaction conditions have been established. The molar absorptivity is (1.6-5.6) x 10 ~ 4 L mol ~ -1) cm -1 .Beer’s law holds for the concentration range of 0.5-11.4 μg mL -1 of Os (Ⅵ).